Composite material turbomachine blade with a reinforced root

ABSTRACT

The invention relates to a turbomachine blade made of composite material including fiber reinforcement, the blade being obtained by three-dimensionally weaving yarns and densifying with a matrix. The blade comprises a single piece constituting both the airfoil and the root of the blade. The blade root has two substantially plane opposite side flanks that are formed in register with the pressure side and suction side surfaces respectively of the airfoil and it is clamped between two metal plates that are fastened against the side flanks of the root.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of composite material turbomachine blades comprising fiber reinforcement densified by a matrix.

The intended field is that of gas turbine blades for aeroengines or for industrial turbines.

Proposals have already been made to make turbomachine blades out of composite material. By way of example, reference may be made to patent application FR 08/58090 (not yet published) filed in the joint names of Snecma and Snecma Propulsion Solide, which application describes fabricating a turbomachine blade by making a fiber preform by three-dimensional weaving and by densifying the preform with a matrix.

Compared with a metal blade obtained in a foundry, a composite material blade presents certain drawbacks associated in particular with mounting it on a metal rotor disk. In particular, a blade obtained by a method as described in document FR 08/58090 generally presents a root of small thickness (less than 5 millimeters (mm) for a low pressure turbine blade). Unfortunately, mounting a blade by engaging its root in an axial slot of a rotor disk requires the blade root to present a certain thickness in order to ensure that the blade is properly held on the disk. Furthermore, the operation of machining the blade root so as to match its profile to the slot in the rotor disk prior to mounting the blade therein is difficult to perform with a blade made of composite material, and runs the risk of damaging the blade. Such an operation necessarily destroys the surface healing layer that is generally deposited on the blade after the preform has been densified. Finally, once mounted on the rotor disk, contact between the metal of the disk and the composite material constituting the blade root gives rise to manifest wear problems due to fretting and due to the differences in thermal expansion between the metal and the composite material.

OBJECT AND SUMMARY OF THE INVENTION

A main aim of the present invention is thus to propose a blade of composite material that does not present the above-mentioned drawbacks.

This object is achieved by means of a turbomachine blade made of composite material, including fiber reinforcement, the blade being obtained by three-dimensionally weaving yarns and densifying with a matrix, and carrying a single piece constituting both the airfoil and the root of the blade, the blade root having two substantially plane opposite side flanks that are formed in register respectively with the pressure side and suction side surfaces of the airfoil, wherein the blade root is clamped between two metal plates that are fastened against the side flanks of the blade root.

The presence of metal plates clamping the blade root presents numerous advantages. In particular, the plates enable the thickness of the blade root to be increased, thereby making the blade easier to mount on a rotor disk. In addition, the plates are easily machined to match the profile of the blade root to the slots in the rotor disk on which the blade is to be mounted. Finally, the use of such metal plates avoids any metal on composite material contact at the blade root, with all the problems to which that gives rise.

According to a particular provision of the invention, one of the metal plates has a rim that is received under the blade root.

At least one of the metal plates may have a hook at an axially downstream end thereof, the hook being designed to receive a retaining ring. Alternatively, at least one of the metal plates may include a notch at an axially downstream end thereof, the notch being designed to co-operate with a tooth of an annular sealing plate.

The metal plates are fastened against the side flanks of the blade root by welding at least one stud that passes through the plates and the blade root in a direction that is substantially perpendicular to its side flanks.

Depending on the shape of the slots in the rotor disks receiving the blade, the metal plates may be machined to be dovetail-shaped.

The invention also provides a turbomachine rotor disk including a plurality of substantially axial metal slots at its outer periphery, wherein the disk further includes a plurality of blades as defined above, each blade having its root mounted in a slot of the disk. The invention provides a turbomachine including at least one such rotor disk.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings that show embodiments having no limiting character. In the figures:

FIG. 1 is a perspective view showing how a turbomachine blade in a first embodiment of the invention is assembled;

FIG. 2 is a perspective view of the FIG. 1 blade once assembled;

FIG. 3 is a longitudinal section view of the FIG. 2 blade;

FIG. 4 is a fragmentary view of a rotor disk provided with blades constituting the first embodiment of the invention;

FIG. 5 is a fragmentary view of a blade mounted on a disk rotor in a second embodiment of the invention;

FIG. 6 is a fragmentary view of a blade mounted on a disk rotor in a third embodiment of the invention; and

FIGS. 7A and 7B are views of blades mounted on a disk rotor in a fourth embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention is applicable to various types of turbomachine blade made of composite material, in particular compressor and turbine blades for different spools of gas turbines, e.g. a rotor disk blade of a low pressure turbine, as shown in FIG. 1.

In known manner, the blade 10 of FIGS. 1 to 4 comprises an airfoil 12, a root 14 formed by a portion of greater thickness and extended by a stilt 16, and a platform 18 situated between the stilt 16 and the airfoil 12. The blade could equally well have a top platform (not shown) in the vicinity of the free end 20 of the airfoil.

The airfoil 12 forms an aerodynamic surface that extends in a longitudinal direction from the platform 18 to its free end 20. It presents a curved profile of varying thickness that is shaped to have a pressure side surface 12 a and a suction side surface 12 b interconnected by a leading edge 12 c and a trailing edge 12 d.

The blade 10 is made of composite material using methods known to the person skilled in the art. By way of example, reference made by made to patent application FR 08/58090 that describes manufacturing such a blade including fiber reinforcement, the blade being obtained by three-dimensionally weaving yarns and densifying with a matrix. With such a method, the portion constituting the airfoil 12 is made integrally with the root 14 of the blade.

Because of the particular way it is fabricated, the blade 10 also presents, at its root 14, two opposite side flanks 22 and 24 that are substantially plane and that lie respectively in register with the pressure side surface 12 a and the suction side surface 12 b of the airfoil 12.

According to the invention, the root 14 of the blade 10 is clamped between two metal plates 26 and 28 that are fastened against the side flanks 22 and 24 of the root.

More precisely, the metal plates 26 and 28 are made of a metal that is compatible with the composite material constituting the blade (e.g. Inconel® for a carbon blade). They are planed and machined so as to cover the surfaces of the side flanks 22 and 24 of the blade root completely.

In the embodiment described herein, the metal plates are fastened by means of at least one through welded stud 30 extending in a direction that is substantially perpendicular to the side flanks, the plates, and an orifice 32 made for this purpose through the root 14 of the blade. The orifice 32 in the blade root is provided during the blade fabrication process, either by using an insert of corresponding shape during weaving, or by drilling through the root after first infiltration.

The metal plates are fastened against the side flanks of the root so as to minimize clearances relative to the root. For this purpose, when using a welded stud, the plates may be put into a press prior to inserting the stud. The stud is then inserted and welded to the metal plates, the welding taking place at a temperature corresponding to the melting temperature of the metal from which the stud is made.

The pressure exerted on the metal plates prior to inserting the stud is a function in particular of the utilization temperature of the blade. The maximum press force for application on the metal plates is thus the product of the acceptable stress (in newtons per square millimeter (N/mm²)) at the utilization temperature multiplied by the surface area (in square millimeters (mm²)) of the side flanks of the root in contact with the metal plates.

Making use of a welded stud to assemble the metal plates together is particularly advantageous. The operation of welding the stud at high temperature has the consequence of the heat energy that is given off being transmitted to the surrounding part so that under the effect of the pressure exerted on the metal plates, the expansion clearance between the parts is filled in. Once the welding operation is over, the assembly shrinks as it cools, thereby further increasing the clamping forces of the metal plates against the blade root.

Naturally, other means for fastening metal plates on the blade root could be used, such as for example fastening by rivet(s) or fastening with the help of at least one screw-and-nut type fastener system.

Furthermore, bonding between the metal plates and the blade root may be improved by degrading the surface states of the faces of the metal plates that face the side flanks of the root.

In addition, as shown in FIGS. 1 to 4, one of the metal plates (specifically here the plate 26) may include a rim 34 that is received under the blade root when the plates are fastened against the side flanks of the root. The rim 34 serves in particular to prevent the metal plates from turning about their clamping axis while the plates are being fastened against the side flanks of the root.

Once the metal plates 26 and 28 have been assembled on the root 14 of the blade 10, they are machined so as to match the profile of the root to the slots in a rotor disk onto which the blade is to be mounted.

Thus, FIG. 4 is a fragmentary radial section through a rotor disk 36 having a plurality of metal slots 38 in its outer periphery each extending in a direction that is substantially parallel to the axis of rotation of the disk. In each of these slots 38, there is mounted a machined root 14 of a blade 10 of the invention.

FIG. 5 is a fragmentary view of a blade 10′ in a second embodiment of the invention that is mounted on a rotor disk 36′.

Compared with the first embodiment, the blade 10′ here described presents a root 14 that is provided with metal plates 26′, 28′ that are fastened against the side flanks thereof by means of two welded studs 30′ (only one being visible in FIG. 5, the other one being offset transversely from the first), which plates are subsequently machined to have a dovetail shape. The blade 10′ is also mounted on a rotor disk 36′ that is provided at its outer periphery with a plurality of axial slots 38′, each having a shape that is complementary to the shape of the machined root of the blade.

FIG. 6 shows a fragment of a blade 10″ in a third embodiment of the invention that is mounted on a rotor disk 36 similar to that described with reference to FIG. 4.

Compared with the first embodiment, the blade 10″ here described differs in that at least one of the metal plates fastened to the root 14 (specifically the metal plate 26″ in FIG. 4) includes a hook 40 at an axially downstream end thereof, which hook is open towards the inside (i.e. towards the axis of rotation of the rotor disk) and serves to receive an annular retaining ring 42. In known manner, such a ring 42 serves to hold the blades axially in the slots 38 of the rotor disk and it contributes to ventilating the blade roots.

FIGS. 7A and 7B are fragmentary views showing a plurality of blades 10″′ in a fourth embodiment of the invention that are mounted on a rotor disk 36 similar to that described with reference to FIG. 4.

Compared with the first embodiment, the blade 10″′ here described differs in that one of the metal plates 26″′ fastened to the root 14 is longer than the other plate 28 (i.e. it projects axially downstream relative to the other plate 28) and has a notch 44 at its downstream axial end for the purpose of co-operating with a tooth 46 on an annular sealing plate 48.

Such an assembly serves to hold the blade 10″′ on the rotor disk 36 by jaw clutching. More precisely, the sealing plate 48 is initially brought against the downstream face of the rotor disk with its teeth 46 positioned between pairs of adjacent blade roots (FIG. 7A). Thereafter, as shown in FIG. 7B, the sealing plate 48 is pivoted angularly about its axis (counterclockwise in FIG. 7B) so that each tooth 46 is received in a notch 44 of the metal plate 26″′ of a blade root, thereby holding the blades axially in the slots 38 of the rotor disk. 

1. A turbomachine blade made of composite material, including fiber reinforcement, the blade being obtained by three-dimensionally weaving yarns and densifying with a matrix, and comprising a single piece constituting both the airfoil and the root of the blade, the blade root having two substantially plane opposite side flanks that are formed in register respectively with the pressure side and suction side surfaces of the airfoil, wherein the blade root is clamped between two metal plates that are fastened against the side flanks of the blade root.
 2. A blade according to claim 1, wherein one of the metal plates has a rim that is received under the blade root.
 3. A blade according to claim 1, wherein at least one of the metal plates has a hook at an axially downstream end thereof, the hook being designed to receive a retaining ring.
 4. A blade according to claim 1, wherein at least one of the metal plates includes a notch at an axially downstream end thereof, the notch being designed to co-operate with a tooth of an annular sealing plate.
 5. A blade according to claim 1, wherein the metal plates are fastened against the side flanks of the blade root by welding at least one stud that passes through the plates and the blade root in a direction that is substantially perpendicular to its side flanks.
 6. A blade according to claim 1, wherein the metal plates are machined to be dovetail-shaped.
 7. A turbomachine rotor disk including a plurality of substantially axial metal slots at its outer periphery, wherein the disk further includes a plurality of blades according to claim 1, each blade having its root mounted in a slot of the disk.
 8. A turbomachine including at least one rotor disk according to claim
 7. 